Electric resistors which are parts necessary for electric circuits have been widely used for any electrical and electronic equipment. Recently, since precision techniques of electrical and electronic equipment have made progress and also electronic equipment for home and industry has attached importance to the safety, the resistors having a fuse function have been required. That is, the resistors including the fuse function in which when the resistors are normally used, good electrical characteristics in TCR (temperature coefficient of resistance) are shown and when an overload is once applied, a fusing is rapidly performed before the overload badly affects other electronic parts must be obtained.
Conventionally, a nickel-iron-phosphorus metal film obtained by an electroless plating process has been proposed as a resistor having excellent fusing characteristics (Japanese patent publication No. 20687 of 1982). It is well known that though a nickel-phosphorus alloy film has the good TCR, the alloy film containing only nickel-phosphorus takes a long time required for fusing and thus an iron is contained as a third component in the above resistor in order to improve the fusing characteristics. However, the iron added as the third component results in the deterioration of the TCR of the alloy film while the addition of the iron to the nickel-phosphorus alloy film allows the fusing time to be reduced surely. That is, in the conventional nickel-phosphorus alloy film resistor, the improvements in both the TCR and the fusing characteristics cannot be attained at the same time, and thus the TCR or the fusing characteristics cannot help deteriorating.
Accordingly, it is an object of the present invention to provide a nickel-phosphorus alloy film resistor having excellent fuse characteristics while maintaining low TCR (temperature coefficient of resistance) characteristics even if a third component such as iron is not contained and a method for producing the alloy film resistor.
It is another object of the present invention to provide a nickel-iron-phosphorus alloy film resistor in which a phenomenon of the increase in current occurs little, which in the case of a nickel-iron-phosphorus alloy film resistor formed by a conventional electroless plating process, it characteristically occurs immediately before the fusing, and to provide a method for producing the alloy film resistor.